Mercury Mechanical Fuel Pump Modifications
 

Has anyone modified their Mercury mechanical fuel pump by adding a diaphragm base from a high performance pump? I am rebuilding my motor and should be somewhere near 700hp when done. I fairly confident the stock fuel pump doesn't have what it needs and I have a GEN V block without the fuel pump mount. I really don't want to go electric if I don't have to, I'm concerned about mounting it in the bilge. What's the most HP anyone has run through the Mercury pump?

Thanks for your help.

If you are talking about the carb pump mounted on the sea water pump, it is a stock BBC pump. Any HP marine BBC pump will work, no need to modify the stock one.

Really
 

No any pump will not work.. I have had good results with pulling the accuator arm out of the Mercury pumps and putting them in a aftermarket hi volume 130gph Carter. Or you can spend the big bucks and go with the KE, but that only flows 120gph.

How does the arm shaft mount in the Carter pump? The shaft is swedged into the housing on the merc pump and you have to wreck the housing to get it out. I actually bought a high volume Holley but the arm shaft was swedged in that on also. I suppose I could drill in to the shaft from both sides and drive the shaft out and then drive the new arm and shaft in and peen the holes over. How did you do it?

+1

Yup
 

Just as you said. Drill it out on the ends (grind the housing flat a little,line it up well and drill). Then I mix up some "good" epoxy and fill the holes. Have two seasons on a couple I have done that way. Sorry about the slow return, long weekend... Pete

I was just looking at my Merc pump and looking at the Carter 120gph version, they are identical. That is except for the hose barb for the vent. I am ordering the Carter and will take both apart side by side and note any differences. At the very least I can use the top of the Merc on the bottom of the Carter.

You can do that also, they are twins to each other. The Carter seam to have a heavier diaphram is why I swap the arms (just me). I also totally tear them down and tap out the inlet and outlet to 3/8" pipe. The only thing that will not work is the extra spring on the outboard part of the arm (Carter). The vent is a easy fix just pull it out carefully and reinstall. Good luck...

The stock Mercury pump is 120gph. I've used them on many 502's with 250 blower/5psi boost with two 850's, making 675-685 hp with a BSFC of nearly .6 with no issue. Much more than that, and I'd go another route. I'm not saying you're doing anything wrong by modifying the pump, just pointing out that the stock pump isn't as bad as many people think... It would run 700hp naturally aspirated without issue, I'm sure.

It's a good idea to ditch the stock Mercury water separator mount as well.

It's a good idea to ditch the stock Mercury water separator mount as well.

Agree with you there for sure..

Was always under the impression the stock units were 80 GPH.

Learn something new every day, thanks Cubic